Generally, in a heat treatment apparatus, an industrial furnace, a firing furnace or the like, a refractory material is provided on the inner wall surface of a heating room. As such a refractory material, a blanket formed of inorganic fibers or the like is known, for example. A flexible refractory material such as a blanket can be easily applied to a curved surface corresponding to the shape of the place of application even when the place of application has a complicated shape.
When the above-mentioned fire refractory material is used as a lining material of a furnace, in particular, it is required to have resistance to wind erosion. Further, the refractory material is required to exhibit desired strength and fire resistance after being applied.
As the blanket used as the base material of a flexible refractory material, one formed of asbestos or ceramic fibers which has a small fiber diameter has heretofore been used. However, in recent years, a problem has been pointed out that inorganic fibers are inhaled by a human body and the inhaled fibers invade the lung. Under such circumstances, bio-soluble inorganic fibers which do not or hardly cause disorders even if inhaled by a human body have been developed (Patent Document 1, for example).
Further, although the invention disclosed in Patent Document 2 relates to mastics, not to a blanket, the document discloses mastics comprising bio-soluble alkaline earth metal silicate fibers and anionic colloidal silica having a pH of 4 to 7. The document states that solidification of the mastics can be prevented by containing anionic colloidal silica having a pH of 4 to 7 as a binder and by further containing a chelating agent, such as EDTA (ethylenediaminetetraacetic acid).